Biochemically, the cerebellum is characterized by a large concentration of cGMP, cAMP, and cGMP-dependent protein kinase. Drug-induced changes in GABA receptor function can be easily monitored by measuring changes in these biochemical parameters. It is suggested that diazepam and muscimol (a modulator and a direct GABA receptor agonist, respectively) modulate cerebellar function by altering the cGMP system. Diphenylhydantoin has its own receptor on cerebellar structures and this receptor is modulated by benzodiazepines. We are now investigating short and long term biochemical changes associated with the stimulation of diphenylhydantoin, receptors and the interrelationship of this receptor with the GABA-benzodiazepine receptor complex.